`(1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90) x = 101010/202020`
`=> ( 1/4.5 + 1/5.6 + 1/6.7 + 1/7.8 + 1/8.9 + 1/9.10) x = (10.10101)/(20 . 10101)`
`=> ( 1/4 - 1/5 + 1/5 - 1/6 +....+ 1/9 - 1/10) x = 1/2`
`=> (1/4 - 1/10) x = 1/2`
`=> ( 10/40 - 4/40) x= 1/2`
`=> 3/20 x = 1/2`
`=> x= 1/2 : 3/20`
`=> x= 1/2 . 20/3`
`=> x= 10/3`
Vậy `x= 10/3`